Today Ethernet forwarding relies on the Rapid Spanning Tree Protocol (RSTP) and the Multiple Spanning Tree Protocol (MSTP), which control forwarding by controlling the active topology. MAC addresses are automatically learnt based on the frames sent on the active topology. RSTP and MSTP are also the main fault handling principles, as they dynamically reconfigure the active topology after a fault.
There is a standardization work going on in IEEE in order to provide a new type of control for Ethernet networks, which is called 802.1Qay Provider Backbone Bridges—Traffic Engineering (PBB-TE) [802.1Qay—Provider Backbone Bridge Traffic Engineering]. In PBB-TE, RSTP and MSTP are not used; instead the forwarding is controlled by the configuration of MAC addresses, i.e. the explicit setting up of forwarding paths towards the destination. That is, no dynamic MAC address learning is applied. The fault handling principle in PBB-TE is protection switching, i.e. switching to a backup path after the failure of a protected network element. Both the working and backup paths are configured in advance.
In this respect, the following issues have been identified by the present applicant.
The protection switching schemes discussed for PBB-TE Ethernet networks rely on switching between end-to-end paths. That is, a failure in the middle of the network has to be first detected by the edge nodes of the network.
The time needed to notify edge nodes may slow down the reaction to the failure (it may depend on the frequency of connectivity monitoring). More significantly, the end-to-end protection schemes require monitoring on a per-connection level. This may result in parallel monitoring of connections.
Mechanisms are known in relation to other packet technologies. For example, Multi Protocol Label Switching (MPLS) Fast Reroute (also called MPLS local restoration or MPLS local protection) is a local restoration network resiliency mechanism. Two methods are defined for MPLS. The one-to-one backup method creates detour Label Switched Paths (LSPs) for each protected LSP at each potential point of local repair. The facility backup method creates a bypass tunnel to protect a potential failure point; by taking advantage of MPLS label stacking, this bypass tunnel can protect a set of LSPs that have similar backup constraints. Both methods can be used to protect links and nodes during network failure.
In addition, IP fast-reroute mechanisms provide protection against link or router failure by invoking locally-determined repair paths. Unlike MPLS Fast Reroute, the mechanisms are applicable to a network employing conventional IP routing and forwarding. IP Fast ReRoute (IP-FRR) mechanisms are meant to provide alternative paths for a temporary time period until the network converges to a stable state with normal forwarding tables. In the interim period, microloops may occur and must be prevented. That is, the IP-FRR mechanisms activate alternate routing paths which avoid micro loops under node or link failures.
However, these alternative technologies differ from Ethernet and, therefore, neither IP nor MPLS FRR mechanisms can be directly applied to Ethernet to alleviate the need of end-to-end per connection monitoring and improve failover times.
It is desirable to address at least one of the above issues.
Methods and apparatus are also known from: [Pan et al. “Fast Reroute Extensions to RSVP-TE for LSP Tunnels” RFC-4090, May 2005] and [M. Shand and S. Bryant “IP Fast Reroute Framework”<draft-ieff-rtgwg-IP-FRR-framework-07.txt> June 2007].